This invention relates to a process for the removal of metals, particularly calcium and iron, from metals-containing petroleum crudes or heavy hydrocarbonaceous residua using oxalic acid as a sequestering or chelating agent. A few, but increasingly important, petroleum crude feedstocks, residua, and deasphalted oil derived from them, contain levels of calcium or iron which render them difficult, if not impossible, to process using conventional refining techniques. The metals contaminants causing particular problems are in the form of non-porphyrin, organometallically-bound compounds. These species have been attributed to either naturally occurring calcium or iron complexes or solubilized calcium from recovery waters which comes in contact with crude oils, or solubilized iron from corrosion and decay of iron-bearing equipment which comes in contact with crude oils. One possible class of calcium or iron-containing compounds identified in particular is the respective naphthenates and their homologous series. These organometallic compounds are not separated from the feedstock by normal desalting processes, and in a conventional refining technique they can cause the very rapid deactivation of hydroprocessing catalysts. Examples of feedstocks demonstrating objectionably high levels of calcium compounds are crudes from China such as Shengli No. 2; examples of high iron-containing crudes include those from San Joaquin Valley in California, generally contained in a pipeline mixture referred to as San Joaquin Valley crude or residuum.
The problems presented by calcium and iron in petroleum feedstocks and the necessity for their removal having only been recently appreciated, and the prior art contains few references specifically to their removal. Metals removal generally using organic compounds, however, has been addressed in the prior art, specifically for the removal of known metallic contaminants, such as nickel, vanadium, and/or copper. The compounds are also ordinarily found in feedstocks as porphyrins and other organometallic compounds.
In U.S. Pat. No. 3,052,627, Lerner, metals-contaminants are removed from crude petroleum feedstocks using a 2-pyrrolidone-alcohol mixture. In U.S. Pat. No. 3,167,500, Payne, metallic contaminants, such as metal-containing porphyrins, are removed from petroleum oils using a condensed polynuclear aromatic compound having a preferred C/H ratio and a molecular weight ordinarily called pitch binders. In U.S. Pat. No. 3,153,623, Eldib et al, selected commercially available organic compounds of high dielectric strength were added to assist in a process basically encompassing the electrically-directed precipitation of metals. U.S. Pat. No. 4,439,345, Duke, discloses the use of carboxylic acids to demulsify by demetalation the middle phase emulsion of an enhanced oil recovery product.
Among other factors, it has now been unexpectedly found that the metals-containing contaminants, particularly those containing calcium and iron, may be effectively removed from the feedstocks of the present invention by binding the metal compounds using oxalic acid and its salts.